Sorry, I garbled some of this a bit.
Suppose, as in OWL-S or SWRL, you have a semantic extension encoded
as a collection of OWL assertions. One way you can mark this, using
my proposal, as mustUnderstand is to mark the pieces of the encoding
as pieces of encoding (e.g., the way you might mark the expansion of
a macro or a auto-generated closure axiom) using a particular
annotation space. That space is marked mustUnderstand.
One could also add a mustUnderstand annotation directly as
convenience syntax.
Cheers,
Bijan.